Displacement pickup



Oct. 31, 1944. NEFF DISPLACEMENT PICKUP Filed Aug. 2, 1945 4 Sheets-Sheet 1 IN V EN TOR.

JOSEPH J IVEFF A T ORNE) Oct. 31, 1944. J. J. NEFF DISPLACEMENT PICKUP Filed Aug. 2, 194;

4 Sheets-Sheet 2 ,INVENTOR. J0$EPH J. NEFF ATTORNEY Oct. 31, 1944. J J NEFF DISPLACEMENT PICKUP Filed Aug. 2, 1945 4 Sheets-Sheet 3 INVENTOR. JOsEPH-J. NEFF.

Oct. 31, 1944. E F 2,361,788

DISPLACEMENT PICKUP Filed Aug. 2, 1943 4 Sheets-Sheet 4 INVENTOR. JOSEPH J. NEFF.

ATTOE/VEK ing illustrated g which:

j PatentecI O'ct 121,119

UNl TED 'isTATas PATE T OFFICE;

2,361,788 DISPLACEMENT. PICKUP Joseph J. Neff, South Euclid, Ohio, assignor, b mesne assignments, to Jack & Heintz, Inc.,

Cleveland, Ohio, a corporation of Ohio Application August 2, 1943, Serial No. 497,087

6 Claims. (01. 73-104) This invention relates to a precision displace 'ment pickup mechanism for indicatingirregularities in worksurfaces.

'It is often desirable to make a precision inspection of finished surfaces to determine their conromance to relatively close tolerance require--' ments. It is, therefore, the primary object of this invention to provide an electrical displacement pickup mechanism capable of measuring or indicating minute irregularities in such surfaces.

A more specificobjectls to provide an electrical displacement pickupinstrument for close inspec tion of geometrically regularly shaped machined metal surfaces to determine whether those sur- "faces are being machined properly and'whether any irregularities such as scratches are present on the contours of such metal surfaces.

With these and other objects in view, the invention resides in the combination of parts and in the details of construction and operation herein-c after set forth'in the following specification and appended claims, certain embodiments thereof bein the accompanying drawings in Figure 1 is asectional view in side elevation of q a displacement pickup mechanism showing a work contacting stylus, a driving coil and two pickup coils, and a stylus controlled armature .mounted centrally with respect to the coils.

Figure 2 is a plan view of the displacement pickup mechanism similar to Figure l.

which may be induced in coils 4 and 2 by driving, coil 3 are equal andare in opposition as a result of the coil connections, thereby neutralizing the effect of the pickup mechanism on the voltmeter.

When pressure is exerted on stylus 2|, armature l I will be moved from its electrical center position so that the voltages induced in coils 2 and 4 by driving coil 3 will become unequal, and the difference in voltage may be measured by an electronic voltmeter or other suitable precision indicating device.

The difference it the magnitude of the induced voltages in coils 2 and4 which results as the armature is moved from its electrical center posi- Figure 3 is a circuit diagram for a displacement pickup instrument including a resistance-condenser tuned oscillator and an electronic voltmeter.

Figure 4 is a view in contour inspecting mechanism having a displacement pickup similar to Figure 1 mounted fixedly thereon. a ,i

Figure 5 is aplan view of a radius contour inspecting mechanism similar to Figure Figure 6 is a view in side elevation ofa radius front elevation of a radius contour inspecting mechanism taken through section 66 of Figure 4.

Referring more particularly to Figure l, a nonconducting casing l is shown supporting two pickup coils 2 and 4, a driving coil 3, contact plates 6, 1 and 8 and two fiexible spring arms 9 and I0 which in turn support a "soft iron armature II by means of pins 12 and I3. Arm [0 projects a predetermined distance beyond casing l and has a stylus 2| fixedly mounted on its extremity. Coil 2 which is shownlconnected by a line 40 to-con tact plate 6 is also connected in series with one tion, is caused by the difference in the lines of force of the field, created by drivingtoil 3, cutting pickup coils 2 .and 4. These lines of force are carried almost entirely by the soft iron armature which forms apart of'the field pattern of the driving coil due to the fact that soft iron has a magnetic permeability several thousand times as great as air. Therefore, if in Figure 1, stylus 2| and arm in are forced downward, then armature II also moves downward,moving the rnagnetic field of driving coil 3 downward with it. More lines of forces are then cutting coil 4 than coil 2 and consequently more voltage'is induced in coil 4than in coil 2.

Alternating current for energizing the driving coil is received from a conventional resistancecapacity turned oscillator which forms a part of the circuit shown in Figure 3. This circuit is connected by means of a transformer 26 to a. standard 110 volt cycle source 25 as shown in the lower right extremity of Figure 3. The alternating current as received by'the transformer is. rectified by a full wave rectifier 30, and the resulting current is then filtered by a filter circuit consisting of a condenser, 3| and a high reactance inductance 32 so that'direct current is supplied to the plates and grids of the various tubes of the oscillator and the voltmeter. The seriesparallel arrangement formed by condenser C2 and resistor Rzxand the condenser Cr and resistor R1 end of coil 4 by means'of aline l8. The other 55. in the oscillator circuit is a positive feedback network which determines the frequency of'oscillation of the oscillator. Resistors Re and R4 creased voltage differential resulting from movement of the armature further out. of the electrical form a negative. feedback network' which stabilizes the frequency and amplitude of oscilla tion. I

Any induced voltage differential occurring be tween coils 2 and 4, due to movement of the armature II from the electrical center. of the three coils, may be measured by a conventional electronic voltmeter such as shown in. Figure 3.

Lines l6 and l! are shown connecting the coilsto a step-up transformer 33. Line I! is also shown' a negative feedback network which stabilizes the amplification of the electronic voltmeter A variable resistor, R5, forms a shunt path for" the milliammeter and is used to adjust its sensitivity.

In order to read directly from the meter 35 the amount of irregularity in a surface, thescale of n the meter is calibrated in thousandths of an inch, butit is understood'that the calibration and sensitivity requireddepend upon the type of sur-- face to be inspected. Although the meter is of a conventional style with zero milliamperes shown normally on the extreme left of the indicating scale and a full scale reading shown on the ex treme right, for this invention a scale is provided dovetailed to sections BI and 62.

62 are moved vertically when adjustment screw 58 is turned and section 62 is moved horizontally bearing pivots 53 and 54 in standards 50. tional View 6 a stylus 2| is shown bearing on a 'hemispherically curved groove 51 in a piece of center of the coils. Figures 4, 5 and 6 show views of, a radius contour inspecting instrument having a displacement pickup mechanism 5| mounted fixedly to an arm 52 which is rotatable about ball work 55. The work 55 is held firmly in position for inspection by work holder 56-whieh is shown mounted on a horizontally and verticall adjustable work table 60. The table 60 is lidably Sections and when adjustment screw 59 is turned. In this manner the groove 51 in work is brought into contact with stylus 2 l exerting enough pressure on the stylus to give azero scale reading on the electronic voltmeter -by means previously described. Since the pickup mechanism 5| is mounted so that the stylus 2l does not coincide with: the axis of rotation of the arm 52 which is through the centers of pivots 53 and 54, but is actually extended beyond that axis of rotation, then the stylus describes a relatively small are when. arm 52 is rotated. 'By varying the position of the pickup mechanism it is readily seen that which has a zero reading at midscale with plus and minus readings in fractional parts of an inch on either side.

In operation the stylus 2| is brought to bear on a. true, reference surface forcing armature ll upward against the positive spring action of arms 9 and it. As previously described, displacement of the armature from its electrical center causes a differential between the induced voltages in coils 2 and 4, said differential being transformed and amplified in the electronic voltmeter circuit.

. The meter indicator 4| is moved toward the right. Enough pressure is applied to the stylus to move the indicator over to a zero reading at midscale. Thus a zero reading is obtained for a desired true reference surface. The displacement pickup is then moved parallel to the surface on which inspection is desired, 'When the stylusis drawn across a scratch on a surface, the armature'under action of spring arms 9 and I ll moves slightly downward, the induced voltages in coils 2 and 4 tend to become more equal and consequently the meter which is set up to read the difference between the two induced voltages indicates a minus reading, since les voltage is transformed by transformer 33. In this manner the depths of scratches on work surfaces are found accurately so as to determine Whether or not they are within desired tolerance-limits to make the work acceptable. ther, stylus 2| leaves the scratch and bears on the reference plane again. The armature is moved upward, the differential of induced voltage in coils 2 and 4 increases and the indicator of meter 35 will move back to its zero or reference reading. In a like manner, apositive readin of the meter is obtained if the stylus is drawn across a ridge above the reference plane,due to an in- As the displacement pickup is moved furarcs of various radii are described by the stylus. However in production inspection of the radius contours of thousands of grooves having equal radii only oneiposition of the pickup mechanism is necessary. I

As the arm 52 is rotated, the stylus moves along the surface of the groove 51. The reading of the electronic voltmeter remains at zero indicating a surface contour of constant radius until such time as the styluscontacts some surface irregularity should there be any present. If an irregularity should be indicated by the electronic voltmeter, the frame 50 is provided with an indexing mechanism 54 for holding the arm 52 firmly in check by notching into groove 65 until a steady and true reading for the particular irregularity can be observed.

It is readily understood that other applications of this displacement pickup mechanism are possible such as the inspection of the internal and external surfaces of tubular devices such as gun barrels, pipes and the like.

I claim:

1. An electrical. displacement pickup mechanism to measure irregularities in geometrically regularly shaped. surfaces comprising an insulating frame, a drivingcoil and two pickup coils, said pickup coils being mounted on opposite sides of said driving coil and all three of said coils being wound about the same axis, an armature mounted centrally with respect to said driving coil and said pickup coils, two spring arms attached to said frame to hold said armature in normal alignment within said coils, and a stylus fixedly mounted on one of said arms to bear on work surfaces and to cause the armature to be displaced from its reference position as said stylus bears on any irregularity on the work surfaces.

2. In an electronic instrument for measuring irregularities on work surfaces, a vacuum tube oscillator, and a vacuum tube voltmeter in combination with a displacement pickup mechanism, said mechanism comprising an insulating frame, a driving coil and two pickup coils, said pickup coils being mounted on opposite sides of said In secdriving coil and all three of said coils being wound about the same vertical axis, an armature mounted centrally with respect to said driving coil and said pickup coils, two spring arms attached to said frame to hold'said armature in normal alignment within said coils at the electrical center of said coils, a stylus fixedly mounted on one of said arms to bear on work surfaces and to cause the armature to be displaced from its electrical center position within said coils as said stylus bearson an irregularity on a work surface leads from thedriving coilconnected to the vacuum tube oscillator circuit to transmit a signal to said driving coil, a lead from one pickup coil to the other to connect said coils in electrical opposition, and leads from the pickup coils con- :nected to thecircuit of the vacuum tube voltsnetertotransmit any differential in voltage,

'induced'by thedriving coil'in said pickup coils V as the armature is displaced from its electrical center by movement of the stylus across an irregularity on a work surface, to the vacuum tube voltmeter. I

3.1;; an electronic instrument comprising a vacuum tube oscillator, a displacement pickup mechanism including a driving coil, a pair of pick-up coils, one of which is located on one side of said "driving coil and the other pick-up coil located on the opposite side of said driving coil, an armature and means for flexibly mounting the same centrallyof said coils, a stylus connected to said armature for moving the same, a vacuum tube voltmeter for the purpose of measuring irregularities on work surfaces, oscillator means to energize 'said driving coil in said displacement pickup mechanism, inductive means to energize in electrical opposition said pickup coils-means responsive to displacement of said'armature in the electrical center of said driving coil" and said pickup coils to cause the magnetic field of said driving coil to shift in thedirection of movement of the armature from its electrical center so that more voltage is induced in one pickup coil than in the other, and vacuum tube voltmeter means to indicate the difference in the magnitude of the induced voltages in said pickup coils.

4. I n'an electronic instrument comprising a vacuum tube oscillator, a displacement pickup tube voltmeter for precision measurement of minute irregularities on'work surfaces, oscillator means to energize said driving coil in the displacement pickup mechanism, inductive means to energize in electrical opposition said pickup coils, means responsive to movement of said stylus on said pickup mechanism across a relatively minute irregularity on a work surface to displace said; armature normally mounted in the electrical center of said driving coil and said pickup coils so that a differential occurs between the voltages induced in said pickup coils by said driving coil, transformer means to stepup said induced voltage differential, amplifier means to receive and amplify said stepped up induced voltage differential from the secondary of said transformer, and vacuum tube voltmeter means to receive said amplified voltage difierential and'to indicate in linear measurement on a calibrated scale the height or depth of an.-irregularity on a work surface asit is traversed by the stylus of the pickup mechanism.

5; In a displacement pickup mechanism comprising an insulated frame, a driving coil, mounted fixedly within said frame, two electrically opposing pickup coils, one mounted on either side of said driving coil'and wound about the same said stylus across an irregularity in a work surface to cause said armature to be displaced from the electrical center of said coils, means to induce unequal voltages in said pickup coils, and means to measure the magnitude of the difference of the induced voltages in said pickup coils.

mechanism including a driving coil, a pair of pick-up coils, one of which is located on one side of said driving coil and the otherpickup 0011 located on the opposite side of said driving coil,

van armature and meansfor flexiblymountin'g the same centrally of said coils, a stylusconnected.

to said armature for moving the same, a vacuum 6. An electrical displacement pickup mechanism to' measure irregularities in geometrically regularly shaped surfaces comprising an insulating frame, a driving coil and a pair of pickup coils, an armature mounted centrally with respect to said driving coil and said pickup coils, resilient means forholding said armature in normal alignment within said coils, and a stylus carried by said resilient means for bearing on work surfaces and causing said armature ,to be bears on an irregularity displaced from its reference position as said stylus onthe work surfaces. JOSEPH J. NEFF. 

